Automatic stove selection system for blast furnaces



06f. 24;'1967 s p KINNEY ET AL 3,348,832

AUTOMATIC STOVE SELECTION SYSTEM FOR BLAST FURNCES Filed Jan. 5, 196e 2 sheets-sh`eet 1 7'0 Rega/aie l 2: I CBTV and MTV VVEIVTORS. SELWYNE? K/N/VEY and HUGH B. CAR/P A f lorneys Oct. 24, 1967 5;,- p, KlNNEY ET AL AUTOMATIC sTovE SELECTION SYSTEM FOR BLAST PURNAcEs Filed'Jan. 5, 1966 2 Sheets-Sheet 2' TTS: Z.v

INVENTORS. SELWYNER K//V/VEY and HUGH .9. CARR BJ M r.

A Hor/lays Patented Oct. 24, 1967 3,348,832 AUTOMATIC STOVE SELECTION SYSTEM FOR BLAST FURNACES Selwyne P. Kinney, Pittsburgh, and Hugh B. Carr, McMurray, Pa., assignors to S. P. Kinney Engineers, Inc., Carnegie, Pa., a corporation of Pennsylvania Filed Jan. 5, 1966, Ser. No. 518,874 6 Claims. (Cl. 266-14) The present invention relates to an automatic system for changing from one stove to another in a multi-stove blast furnace installation, and particularly to a means for selecting the hottest of the stoves as the stove next to go ON BLAST.

In a blast furnace installation, hot blast is supplied to the furnace from a plurality of hot blast stoves which are arranged so that one stove at a time supplies the hot blast while the remaining stove or stoves are being heated by their respective burners to subsequently be put on blast. Generally, it is desirable to deliver the hot blast at a uniform ow rate and temperature, sometimes called the straight line heat method. Smooth and eicient operation of the blast furnace depends, to a large extent, on this uniformity of hot blast fiow andtemperature.

Most. modern blast furnace installations employ three or four stoves to supply the hot blast, however, for convenience'the description herein will be addressed to an installation having three stoves, it being understood that the system could be adapted for different numbers of stoves.

. As is known in the'art, a stove is heated by burning gases in a combustion chamber and storing the heat in a checkerwork chamber of refractory bricks. The heat thus stored is supplied to a blast furnace by forcing unheated air through the stove checkerwork to heat the air which then becomes the hot blast supplied to the furnace.

When a stove is supplying the hot blast, it is said to be ON BLAST. When it is being heated, it is said to be ON GAS. When a stove has been heated sufliciently to go ON BLAST, but is not yet needed, it can be placed in an ON BOTTLED status, which is a passive condition designed simply to retain the heat in the stove until it is needed for the hot blast.

Earlier stove changing systems having automatic features have been designed to select, as the stove to next go ON BLAST, the stove which has been ON GAS the longest period of time, i.e., the stoves are `always selected in rotation in an unchanging order. However, for maximum efficiency of the overall installation, the hottest stove should be selected as the one to go ON BLAST, and this may not always be the one next in order of rotation. The present invention provides a system which automatically selects the hottest stove as the stove next to go ON BLAST, regardless of how long it may have been ON GAS. While the selected stove may frequently be the one which has been ON GAS the longest, this is not necessarily the case. The switch from one stove to another involves the operation in proper sequence of several large valves, now generally operated by electric motor powered mechanism.

The invention disclosed is employed in connection with a exible stove changing system having three modes of operation: REMOTE, SEMI-AUTOMATIC AND AUTOMATIC. l

REMOTE operation is designed for maintenance purposes and permits the various valve drives to be operated by push button controls at or near the particular mechanism to be checked. In the mode, the drives of a given stove are not interlocked in any manner, either with other drives of the saine stove or those of any other stove. A stove may be switched to REMOTE at any time,

and al1 SEMI-AUTOMATIC and AUTOMA'ITC circuits will be de-energized.

The SEMI-AUTOMATIC mode is used when all of the stoves cannot be operated automatically -as a system. In this mode, the drives of a given stove are all interlocked; and all stoves operating semi-automatically are interlocked. A stove may be switched to SEMI-AUTOMATIC yat any time and the REMOTE circuits will be de-energized so that individual push-button control will be ineffective.

The AUTOMATIC mode is intended as the normal mode of operation in which the stoves are sequenced automatically to maintain a predetermined hot blast teniperature. All the stoves must be on AUTOMATIC for the system to operate and 4all the stoves must be on SEMI-AUTOMATIC in order to switch to AUTO- MATIC. In this mode all drives are interlocked. The system is designed to detect the temperature of the hot lblast coming from the stove then ON BLAST and to initiate a stove changing sequence when the stove then ON BLAST can no longer supply hot blast at the predetermined temperature. The system detects and compares the temperatures of the stoves and selects the hottest of these to ON BLAST and initiates all the valve closings and openings necessary to effect a smooth changeover while maintaining a continuous hot blast to the furnace.

An object of the invention is to provide a new and useful control system for changing stoves in a multistove blast furnace installation.

Another object is to provide a control system which insures the continuous uniform supply of hot blast from a plurality of stoves in a blast furnace installation.

Another object is to provide in a vmulti-stove blast furnace installation, an automatic stove changing system which selects the hottest of the stoves as the next stove to go ON BLAST.

These and other objects will be apparent to those skilled in the art and more readily understood by refp erence to the following description wherein:

FIG. 1 is a schematic illustration of furnace installation;

FIG. 2 is a block diagram of an automatic ystove changing system incorporating the stove selection circuitry of the invention; and

FIG. 3 is a schematic diagram of the stove selection circuitry.

Referring first to FIG. l there is shown a schematic layout of a typical three stove blast furnace installation. The blast furnace itself is represented here by the bustle pipe 10. The three stoves are indicated by the Roman numerals I, II and III, which numerals will be retained throughout to indicate the various valves and relays associated with a particular stove. Each stove has a combustion chamber 11 and a checker chamber 12. Gases burned in the combustion chamber pass upwardly to the dome of the stove, then downwardly through the checkerwork where the heat is stored in refractory checker bricks, thence out through a chimney valve CH to a stack (not shown). Each stove has two chimney 4valves but for convenience, only one valve is shown. l

There is a cold blast main 13-having branches 14 leading to the bottom of the checker chamber of each stove and a branch 15 which is the mixer line. 'From the lower part of the combustion chamber of each stove there is a hot blast exit -line 16 which opens into the hot blast main 17. Each stove has a hot blast valve HB in its hot blast exit line and a cold blast shut-olf valve CBSO in its cold blast line. The mixer line 15 has branches 18 opening into the hot blast exit line 16 of each stove on the stove side of the hot blast valves. Between the main mixer line and the hot blast exit lines 16, each stove a multi-stove blast has a mixer shut-olf valve MSO in its mixer vbranch line 18.

A mixer throttling valve MTV is located in the mixer line intermediate the cold blast main 13 and the tirst mixer shut-off valve, in the case MSO-III. A cold blast throttling valve CBTV is located in the cold blast main up stream of the stove branch lines 14. Each stove has a burner air duct 19, through which air is forcibly supplied to the combustion chamber by means of a blower 20.`On the stove side of the blower there is a combustion air regulating valve CARV. Opening into the air duct 19, intermediate the air regulating valve CARV and the burner shut-off valve BSO, there is a burner gas line 21 for supplying the gas to be mixed with the air for burning in the combustion chamber. In the gas line 21 there is a gas regulating valve GRV. Intermediate the gas regulating valve GRV and the air duct 19, there is a gas shut-off valve GSO.

Near the bustle pipe 10 in the hot blast main 17, there is a temperature sensing device 22 for a purpose to be explained later. On the stove side of the chimney valve CH of each stove there is another temperature sensing and indicating device23, which provides the signals to be compared in the selection of the stove to go ON BLAST as will be more fully explained later.

Assuming that stove I is ON GAS and is to be placed ON BLAST, the operation and positions of the various valves associated therewith will now be explained.

(1) Gas shut-off valve GSO-I is closed,

(2) Burner shut-olf valve BSO-I is closed,

(3) Chimney valve CH-I closed,

(4) Cold Blast shut-off valve CBSO-I opened, (5) Hot blast valve HB-I opened,

(6) Mixer shut-off valve MSO-I opened.

two throttling valves are regulated in response to the tem` perature signals developed by the sensing device 22 in the hot blast main 17. When a large portion of the cold blast entering the stove passes through the checkerwork 12, is heated, leaves the stove to enter the hot blast exit line 16 where it is mixed with the by-passed air, and thence passes into the hot blast main 17 to the bustle pipe 10. The device 22 senses the hot blast temperature and generates an electrical signal which regulates the cold blast throttling valve CBTV and mixer throttling valve MTV to maintain the desired preselected hot blast temperature. The regulation of the throttling valves CBTV and MTVis accomplished in two stages. In the rst stage, when the stove ishottest, the valve CBTV is gradually opened to its full open position thereby circulating a greater percentage of the cold blast through the stove as the stove cools. When the valve CBTV is fully open, the second stage begins, during which the mixer valve MTV is gradually closed thereby decreasing the mixing air until substantially all of the cold blast is passed through thel stove checkerwork. The closing of the mixer throttling valve MTV signifies that the stove can no longer supply the hot blast at the required temperature, and signals the start of the selection `and change-over sequence. All the stoves operate in the manner just described when ON BLAST.

When the stove is placed in ON GAS from ON BLAST, the following sequence is observed:

(1) I-Iot blast valve HB-I and mixer shut-olf valve MSO-I closed, l

(2) Cold blast shut-olf valve CBSO-I closed,

(3) Chimney valve CH-I opened,

(4) Burner shut-olf valve BSOI opened,

(5) Gas shut-off valve GSO-I opened.`

To place the stove in ON BOTTLED status from ON GAS, the following sequence takes place:

the stove is rst put ON BLAST,

( 1) vGas shut-off valve GSO-I closed, (2) Burnershut-otf valve BSO-I closed, (3) Chimney valve CH-I closed.

It will be observed that these last steps are the first steps in proceeding from ON GAS to ON BLAST, consequently in going from ON BOTTLED to ON BLAST the sequence is the same as in ON GAS to ON BLAST except that the above three steps have already been performed, so it is necessary only to open the cold blast, hot blast and mixer shut-ofrr valves.

The foregoing description forms no part of the present invention per se but is included to more clearly set forth the background for the invention.

FIG. 2 illustrates in blockdiagram an automatic stove changing system incorporating the selection circuitry 24 of the invention. The blocks indicating the stoves I, II and Ill also include all of the valves, drive mechanisms, etc., which are sequenced and controlled by the automatic stove change-over control circuitry of block 24a. The stove blocks also include the stove temperature sensing and in-v -II, or -III in the control circuitry ON BLAST the stove whose temperature signal corresponds to the selection circuit output signal.

Referring to FIG. 3 the selection circuitry itself is designated as 24 and is enclosed by the dotted lines. The remaining circuitry comprises the input and output circuitry for the stove selection circuitry-24. All relay contacts in FIG. 3 as well as throughout the description, are shown in the de-energized position.

As before stated when the mixer throttling valve MTV reaches itsv maximum closed position the stove then ON- BLAST can no longer supply the propertemperature of hot blast and a new stove is required. The selection sequence is initiated by the closing of contacts 25 of a limit switch on the mixer throttling valve MTV. Meanwhile, the temperature of each stove is being sensed by the ternperature sensing and indicating devices 23-1, -II and the indicating portions of which are illustrated in FIG. 3

The series contacts 26, 27 and `28 are all normally` closed when the system is in AUTOMATIC, as they must be for the selection circuit to operate. All the relays K1, K2, K3, K4, and T5 are initially de-energized until closure of contacts 25,` whereupon time delay relay T 5 is energized thereby instituting a predetermined time delay of approximately fifteen seconds on expiration of which contacts T5-1 are closed. During this time delay the ternperature signals from the stoves are being compared in the detecting relay 26. In the circuitry shown, the com.- parison sequence is always the same, regardless of which stove is ON BLAST. Stoves I and II are first compared, the temperature signals from to the detecting relay 26 through the closed contacts K3-1 and K2-1 respectively.

If stove I is hotter, the RH side of relay 26 will ener-tl gize to operate the contacts f RH-l and RH-2. When this occurs relay K2 will energize through RL-l, cross connecting lead 30, RH-2, K3-3 and KZ-S and be locked in by the holding circuit through contacts K2-4. At the Sametime, relay K1 will temporarily energize ,but will drop out when the RH signal is removed by the opening of contacts K2-1 in the line from stove II to the detecting relay 26. Note that no stove selection is yet made output signal actuating one of the- 23-1 and 23-11 being sent ing device 23-III being connected to the detecting relay 26 through the n-ow-closed contacts K2-2. If stove I is still the hottest, the RH side of relay 26 will again energize relay'Kl (relay K2 is already energized) thereby closing contacts K1-1. Thus when timer T5 Yruns out, stove I will be selected by energizing the selection relay SR-I through the closed contacts TS-l, K2-6 and K1-1.

If, when comparing stoves I and III, stove III had been the hottest, the RL side of relay 26 would energize thereby energizing relay K4 through RH-l, lead 30 and RL-Z. This results in the selection of stove III by energizing relay SR-III through T-1, K2-6 and K4-1. Note that relay K3 will not energize when K4 is energized because the contacts K2-5 are open since relay K2 is energized by the holding circuit through contacts K2-4.

If stove II had been hottest in the rst comparison, relays K3 and K4 would be energized through RH-l, lead 30, RL-2, KZ-S and K3-5. Relay K3 would -be locked in by the holding circuit through K3-4 and relay K4 would be temporarily energized as explained before in connection with relay K1. Stove II and III would then be compared, stove II being connected to relay 26 through K2-1 and stove III through the now closed contacts K3-2.

If stove II is hotter the RL contacts are again operated energizing relay K4 (K3 already being energized). Thus when T5 runs out stove II will be selected by energizing selection relay SR-II through TS-l, K3-6 and K4-2.

If stove III is hotter than stove II then the RH contacts are operated, energizing relay K1 through RL-l, lead 30 and RH-2. Relay K2 will not energize because contacts K3-3 are open, relay K3 being energized by the holding circuit through contacts K34. It is obvious then that stove III Will be selected by the energizing of relay SR-III through T5-1, K3-6 and K1-2.

The summary of the described selection sequence is as follows: stoves I and II are compared, the hottest of these is compared with stove III and the hottest of these latter is selected as the stove next to go ON BLAST.

The energization of the selection relay by the output signal from the selection circuitry 24 sets up the actual control circuitry 24a for changing over from one stove to another. Such circuitry is already known in the art and is not set forth in detail here for purposes of brevity and so as not to unduly prolong the specication with extraneous material. However, one such system may be seen in the U.S. patent to Jansen et al., No. 3,034,775, issued May l5, 1962.

It will be understood that the selection relay SR which has been energized by the selection circuit 24 will remain so energized until the mixer throttling valve MTV again opens, thereby opening limit switch 25. Of course, the selection relays SR, when actuated, energize various holding circuits in the control circuitry so the selected stove and its various valve drives and so forth will remain in the proper state of energization or de-energization, as the case may be, even though all the selection relays SR are de-energized when limit switch 25 opens.

The opening of the limit switch 25 restores all the relays of FIG. 3 except A.C. detecting relay 26 to the de-energizing state as shown, thereby readying the circuit for another selection when the limit switch 25 again closes. In the circuit of FIG. 3, when the system is in AUTOMATIC detecting relay 26 will always` be energized in either the RH or RL side but the contacts thereof are, nevertheless, all shown in the de-energized state for clarity of description.

While we have shown one embodiment of the invention, it will be obvious to those skilled in the art that variations and modifications in the particular construction and arrangement of parts can be made within the scope and spirit of the invention and that the invention may be adapted to different numbers of stoves.

We claim:

1. In a multi-stove blast furnace installation of the type described, apparatus for automatically selecting the hottest of the stoves as the stove next to go ON BLAST,

comprising,

(a) means sensing the temperatures of the stoves and generating a signal indicative of the temperature of each stove,

(b) means for comparing the temperature indicative signals and producing an output signal indicative ofthe hottest of the stoves, and

(c) means responsive to the output signal for establishing as the stove next to go ON BLAST, the stove whose temperature indication produced the output signal.

2. In a multi-stove blast furnace installation of the type described, apparatus for automatically selecting the hottest of the stoves as the stove next to go ON BLAST, comprising,

(a) means sensing the temperatures of the stoves and generating a signal indicative of the temperature of each stove,

(b) means for comparing the-temperature indicative signals from a selected plurality of the stoves, but less than all the stoves, and producing an output signal indicative of the hottest of the selected plurality of stoves,

(c) iirst circuit means for enabling passage of selected pluralities of temperature indicative signals to the comparing means,

(d) second circuit means, conditioned by the output signal from the comparing means, for conditioning the first circuit means to enable passage to the comparing means of selected pluralities of the temperature indicative signals, the selected pluralities comprising a lirst pre-selected plurality and a succeeding plurality including the highest temperature signal of the preceding plurality and a remaining previously unselected temperature signal, the second circuit means continuing to so condition the rst circuit means until the temperature signal from each stove has been compared at least once with the temperature signal from at least one other stove, and

(e) means responsive to the comparing means output signal at the termination of the comparing sequence for establishing as the stove next to go ON BLAST, the stove whose temperature corresponds to the output signal at that time.

3. In a multi-stove blast furnace installation of the type described, apparatus for automatically selecting the hottest of the stoves as the stove next to go ON BLAST, comprising,

(a) means generating a signal from each stove indicative of the stove temperature,

(b) means for comparing the temperature indicative signals and producing an output signal indicative of the hottest ofthe stoves,

(c) means responsive to the output signal for establishing as the stove next to go ON BLAST, the stove whose temperature corresponds to the output signal, and

(d) means actuated by the detection of the inability of the stove then ON BLAST to continue to supply the hot blast at a predetermined temperature for enabling passage of the output signal from the comparing means to the responsive means.

4. In a three-stove blast furnace installation, apparatus for automatically selecting the hottest of the stoves as the stove next to go ON BLAST, comprising,

(a) means sensing the temperatures of the stoves and generating electrical signals indicative of the temperature of each stove,

(b) means for comparing the temperature signals from any two of the stoves and producing an output signal indicative of the hottest of the compared stove temperatures,

(c) means for sequencing the comparison means to compare the temperature of the hottest of the first two compared stoves with the temperature of the t remaining stove, and

(d) means responsive to the signal produced by the comparing means on comparison of the temperatures of the hottest of the rst two compared stoves with the temperature of the remaining stove for establishing as the stove next to go ON BLAST, the stove whose temperature corresponds to the last mentioned si nal.

5. Iigl a three-stove blast furnace installation wherein one of the stoves is currently-ON BLAST, apparatus for automatically selecting the hottest of the stoves, as the stove next to go ON BLAS'lcomprising,

(a) rst circuit means including,

(1) means sensing the temperature of each stove and generating electrical. signals indicative of the temperature of each stove,

(2) means for comparing the temperature signals from any two of the stoves and producing an output signal indicative of the hottest of the compared stoves,

(3) means enabling the passage of any two of the temperature indicative signals to the comparing means,

(b) second circuit means, including,

(1) means sequencing the first circuit enabling means to cause the first circuit comparing means to compare the temperature of the hottest of the first two compared stoves with the temperature of the remaining stove,

(2) means detecting the inability of the stove then ON BLAST to continue to supply the hot blast at a predetermined temperature for actuating the vthe sequencing means, and (c) third circuit means, including,

(1) means responsive to the output signal froml the comparing means on comparison ofthe temperature of the hottest of the first two cornpared stoves with the temperature of the remaining stove for establishing `as the stove nextto go ON BLAST, the stove whose temperature corresponds to the last mentioned output signal, and

(2) means enabling the passage of the output signal to the responsive means.

6. The combination as deiined in claim 5 including time ydelay means actuated by the second circuit detecting means for inhibiting passage of an output signal to the responsive means for a period sufficient to enable the rst and second circuit means to compare the temperature signals from each stove with the temperature signal from at least one other stove.

References Cited UNITED STATES PATENTS 2,931,635 4/1960 Bran et al 263-19 3,034,775 4/1962 Jansen et al 266-14 XR 3,153,532 10/1964 Touzalin 263-19 3,178,160 4/1965 Walther et al 266-14 XR 3,180,629 4/1965 Goeke et al 266-14 XR 3,199,849 8/1965 Koinis 263-19 I. SPENCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, Assistant Examiner. 

1. IN A MULTI-STOVE BLAST FURNACE INSTALLATION OF THE TYPE DESCRIBED, APPARATUS FOR AUTOMATICALLY SELECTING THE HOTTEST OF THE STOVES AS THE STOVE NEX TO GO ON BLAST, COMPRISING, (A) MEANS SENSING THE TEMPERATURE OF THE STOVES AND GENERATING A SIGNAL INDICATIVE TO THE TEMPERATURE OF EACH STOVE, (B) MEANS FOR COMPARING THE TEMPERATURE INDICATIVE SIGNALS AND PRODUCING AN OUTPUT SIGNAL INDICATIVE OF THE HOTTEST OF THE STOVES, AND 